Tie plate damage to wooden crossties through crosstie surface abrasion is a significant form of distress negatively impacting crosstie condition by reducing rail fastener holding capabilities. Referring to FIG. 1, a typical rail assembly includes a rail 100 resting on top of a tie plate 102 (also referred to as a “rail plate” or “base plate”) and a plurality of spikes 104 securing the tie plate 102 and rail 100 to a crosstie 106, such as a wooden crosstie. The amount that a base of the tie plate 102 (i.e., a tie plate base 108) has penetrated or cut into a surface of the underlying wooden crosstie 106 is due to repeatedly applied heavy loads from train traffic and is referred to as the level of “Plate Cut” (the amount the tie plate base 108 has cut or abraded into a surface of the crosstie 106).
The rail 100 includes a rail head 110 located at a top of the rail 100, a rail web 112, and a rail foot 114 located below the rail web 112 and the rail head 110. A bottom of the rail foot 114 is referred to as a rail base seat 116, and a top of the rail foot 114 is referred to as a rail base surface 118.
Employing current three-dimensional (3D) triangulation-based measurement technologies used for railway track assessment with 3D sensors positioned above the rail assembly, an elevation of the rail base seat 116, or the tie plate base 108 cannot be measured directly. Therefore, an elevation of the tie plate base 108 must be estimated by measuring an elevation of a top surface of the tie plate 102 (i.e., the tie plate surface 120) and subtracting an estimated thickness of the tie plate 102.
The plate cut value increases as the tie plate 102 cuts downward into an upper surface of the crosstie 106 to which the tie plate 102 is fastened (the tie plate base 108 penetrates or cuts into the upper crosstie surface 122). Conventional methods of determining plate cut value require calculating the difference between the surface elevation of outermost tie plate edges (on the “field” side outside of the rails and on the “gauge” side that is between the rails) and the adjacent upper crosstie surface 122 elevations near the edge of the tie plate 102. Referring to FIG. 2, a conventional plate cut measure is derived from the difference in elevation between tie plate surface 120 and the adjacent crosstie surface elevation (i.e., the upper crosstie surface 122). In situations where the tie plate and crosstie surface regions are not obscured, plate cut can be calculated as follows:Plate Cut=Crosstie Surface Elevation−(Plate Surface Elevation−Plate Thickness Estimate)  Equation 1:
A plate cut value of 0 millimeters (mm) would represent an undamaged (new) crosstie surface, as shown in FIG. 2. Referring to FIG. 3, in contrast to a new crosstie, a plate cut value of 25 mm or greater would represent a significant amount of damage to the crosstie surface. In practice, it is common to have significant amounts of ballast 124 or other track debris obscuring the tie plate 102 surface for significant portions of a rail network, as illustrated in FIG. 4. The presence of any material on the tie plate surface 120 makes it difficult, if not impossible, to determine the plate surface elevation in debris occluded areas. Without the ability to determine elevations of the tie plate surface 120 (for either the field and gauge side), a plate cut value cannot be determined.
In addition to plate cut in wooden crossties, concrete crosstie surface abrasion is a significant form of distress which negatively impacts concrete crosstie condition. Referring to FIG. 5, rail assemblies may also be formed using a concrete crosstie 126. The rail 100 rests on top of a pad 128 located between a rail base seat 130 and an upper crosstie surface 132 of the concrete crosstie 126. A clip 134 secures the rail 100 to the concrete crosstie 126 and includes an insulator 136 located between the clip 134 and the rail 100. Rail seat abrasion reduces rail fastener downward force on a rail foot 138 of the rail 100, thereby reducing the capability of the clip 134 to secure the rail 100 to the concrete crosstie 126. The pad 128 placed under rail 100 protects the upper crosstie surface 132 from rail movements due to applied loads from train traffic and from rail movement due to rail thermal expansion and contraction. The pad 128 wears until the pad thickness is diminished to the point where the rail base seat 130 is able to contact the upper crosstie surface 132. The amount that the rail base seat has penetrated or abraded the underlying crosstie surface is referred to as the level of rail seat abrasion.
Employing 3D triangulation-based measurement technologies used for railway track assessment with sensors positioned above the track surface, the elevation of the rail base seat 130, or the rail pad thickness cannot be measured directly. Therefore, the rail base seat elevation must be estimated by measuring a rail base surface elevation 140 and subtracting an estimated rail base thickness.
As a rail base seat wears the underlying pad 128, the pad thickness is reduced to zero. At the point of a zero thickness pad, the rail seat abrasion is said to be 0 mm, representing the point at which the rail base seat 130 is beginning to contact the upper crosstie surface 132. As the rail base seat 130 continues to abrade and penetrate into the upper crosstie surface 132, the rail seat abrasion values increase.
The conventional method of determining the rail seat abrasion parameter requires calculating the difference between the rail base seat elevation (for the field and the gauge sides of the rail) and the adjacent crosstie surface field and gauge elevations near the rail base, as shown in FIGS. 6 and 7. The conventional method of calculating rail seat abrasion is based on the elevation difference between the rail base surface and the adjacent crosstie surface. In situations where the rail base and crosstie surface regions are not obscured, rail seat abrasion is calculated as follows:Rail Seat Abrasion=Crosstie Surface Elevation−(Rail Base Surface Elevation−Rail Base Thickness Estimate)  Equation 2:
In practice, it is common to have significant amounts of ballast 124 or other track debris obscuring the rail base surface for substantial portions of a rail network, as illustrated in FIG. 8. The presence of any material on the rail base surface makes it difficult, if not impossible, to determine the rail base surface elevation in debris occluded areas. Without the ability to determine elevations of the rail base surface (for either the field or gauge side), a rail seat abrasion value cannot be determined.
What is needed, therefore, is a means to measure plate cut and rail seat abrasion values in all track conditions. The capability to determine elevations for all crosstie plates and rail base surfaces regardless of whether they are obscured by ballast or other debris would significantly improve the ability to report plate cut measures for all wooden crossties and rail seat abrasion measures for all concrete crossties in a rail owner's network.